Today in most geothermal heat- and water supply plants provision is made for the return of the brine used therein into a geothermal deposit. Centrifugal pumps are used for those purposes as well as for transporting hot brine to consumers. These pumps feature high metal intensity and short service life under the conditions of work with hot brines. For these same purposes in a number of plants use is made of heat pumps which are more reliable and durable compared to centrifugal ones, but require greater power consumption. Therefore, capacity and economical efficiency are the principal requirements set to geothermal plants.
Known in the art is a heat- and water supply plant using the heat of a geothermal source (SU, A, No. 823762). The plane incorporates a geothermal source with which the main and auxiliary heat pumps communicate, the water from the outlet of the first pump being fed to a hot water supply system and from the outlet of the second one--to a water tower designed to deliver water to a process--potable water supply system. Each heat pump comprises a condenser, an evaporator and a compressor with an electric drive. A heat supply system boiler communicates with the geothermal source via the main heat pump condenser. The plant also has a cooling chamber arranged between the evaporator and the main heat pump condenser. The evaporator of the auxiliary heat pump communicates with the main heat pump condenser via a three-way cock and a check valve.
In winter time the prior art plant is used for heating which is effected by means of the main heat pump and hot water supply using an auxiliary heat pump. In summer the heating system is cut off and the main heat pump is connected to the cooling chamber. An increase in refrigerating capacity of the main heat pump, as well as the plant efficiency, when the latter operates in summer time, are ensured by feeding the water, preheated in the auxiliary heat pump evaporator, to the main heat pump condenser.
In winter time, it is impossible to increase efficiency of the prior art plant.
Besides, using an electrically driven compressor in the heat pumps of the prior art plant calls into play additional power sources which impairs its efficiency. Note that in the hot water supply system use is made of the water of the same chemical composition as in the geothermal source which normally features a high content of mineral salts. In the prior art plant there is not provision for the return of water to the geothermal deposit after it is used in the heat supply system. This means that a long operation of the geothermal deposit depletes its reserves and brings about salinization of soil.
The geothermal heat and water supply plant (SU, A, No. 1134854) allows for the return of the used brine to the geothermal deposit. The plant comprises a geothermal well to extract the brine in the form of a steam-and-fluid mixture communicating with the separator which in the steam phase communicates with a jet pump and with a high-pressure stage of the injector, communicating with a pipeline for transporting water after it is used in the heat supply system, and in the fluid phase--with the cooled side of the heat exchanger communicating with a jet pump whose outlet communicates with a well for pumping the brine liquid phase, and a fresh water source communicating with the heated side of the heat exchanger which, in turn, communicates with the low pressure stage of the injector from the outlet of which the water is drawn into the heat- and hot water supply systems.
In the prior art plant the brine is supplied from the jet pump outlet directly into the well to pump the brine fluid phase, while the water, once used in the heat supply system, is fed to the high pressure stage of the injector. By virtue of the injector the water is circulated in the heat supply system and fresh water is taken from the source. Once used in the heat supply system, the water returning to the high pressure stage has a fairly high temperature which determines the pressure corresponding to this temperature. Given appreciable pressure in the high pressure stage of the injector, the latter shows unstable operation, consuming less amount of steam and fresh water, which reduces pressure at the injector outlet and diminishes the plant capacity as a whole.
In the prior art plant the jet pump is designed to pump the brine fluid phase to a geothermal deposit. To overcome the well resistance, one should provide pressure at the jet pump outlet the value of which is specified by the amount of steam fed thereto.
An elevation of pressure of the brine being pumped by increasing the steam consumption brings about a decline in the amount of steam fed to the injector and the latter's unstable operation. In addition, the brine temperature at the pumping well inlet is insignificant which creates additional resistance caused by a high viscosity of the brine.
Thus, in the known plant the geothermal deposit thermal energy is used ineffectively, thus impairing the plant efficiency.